Technology and Health Care - Volume 16, issue 1

Authors: Lozano, S. | Möller, K. | Brendle, A. | Gottlieb, D. | Schumann, S. | Stahl, C.A. | Guttmann, J.

Article Type: Research Article

Abstract: A closed-loop system (AUTOPILOT-BT) for the control of mechanical ventilation was designed to: 1) autonomously achieve goals specified by the clinician, 2) optimize the ventilator settings with respect to the underlying disease and 3) automatically adapt to the individual properties and specific disease status of the patient. The current realization focuses on arterial oxygen saturation (SpO2 ), end-tidal CO2 pressure (Pet CO2 ), and positive end-expiratory pressure (PEEP) maximizing respiratory system compliance (Crs ). The “AUTOPILOT-BT” incorporates two different knowledge sources: a fuzzy logic control reflecting expert knowledge and a mathematical model based system that provides individualized patient specific …information. A first evaluation test with respect to desired end-tidal-CO2 -level was accomplished using an experimental setup to simulate three different metabolic CO2 production rates by means of a physical lung simulator. The outcome of ventilator settings made by the “AUTOPILOT-BT” system was compared to those produced by clinicians. The model based control system proved to be superior to the clinicians as well as to a pure fuzzy logic based control with respect to precision and required settling time into the optimal ventilation state. Show more

Keywords: Mechanical ventilation, closed-loop system, adaptive controller, physiological model, fuzzy logic

DOI: 10.3233/THC-2008-16101

Citation: Technology and Health Care, vol. 16, no. 1, pp. 1-11, 2008

Authors: Ryf, Salome | Wolber, Thomas | Duru, Firat | Luechinger, Roger

Article Type: Research Article

Abstract: Permanent magnets may interfere with the function of cardiac pacemakers and implantable cardioverter-defibrillators (ICDs). Neodymium-iron-boron (NdFeB) magnets have become widely available in recent years and are incorporated in various articles of daily life. We conducted an in-vitro study to evaluate the ability of NdFeB magnets for home and office use to cause interference with cardiac pacemakers and ICDs. The magnetic fields of ten NdFeB magnets of different size and shape were measured at increasing distances beginning from the surface until a field-strength (B-field) value of 0.5 mT was reached. Furthermore, for each magnet the distance was determined at which a …sample pacemaker switched from magnet mode to normal mode. Depending on the size and remanence of individual magnets, a B-field value of 0.5 mT was found at distances ranging from 1.5 cm to 30 cm and a value of 1 mT at distances from 1 cm to 22 cm. The pacemaker behavior was influenced at distances from 1 cm to 24 cm. NdFeB magnets for home and office use may cause interference with cardiac pacemakers and ICDs at distances up to 24 centimeters. Patient education and product declarations should include information about the risk associated with these magnets. Show more

Keywords: Pacemaker, implantable cardioverter-defibrillator, EMI, neodymium magnet

DOI: 10.3233/THC-2008-16102

Citation: Technology and Health Care, vol. 16, no. 1, pp. 13-18, 2008

Authors: Mootanah, Rajshree | Jarrett, Paul | Ingle, Paul | Cheah, Kevin | Dowell, John K. | Shelton, Julia C.

Article Type: Research Article

Abstract: Although surgical fixation techniques are major contributing factors to the survivorship of total hip replacements, they vary considerably among orthopaedic surgeons. We investigated the effect of the following configuration of anchorage holes on the stability of acetabular component fixation: 3 × 12 mm, 3 × 6 mm, 6 × 6 mm, and 12 × 6 mm. The reconstructed acetabulae were tested to torque failure, whilst being subjected to a compressive load of 2.1 KN. Higher torque to failure values were obtained for specimens with three 12 mm anchorage holes, compared with six or more 6 mm anchorage holes and were …in line with our computer simulation results. We propose that the longevity of cemented total hip replacements could be improved by drilling a few large anchorage holes. Show more

DOI: 10.3233/THC-2008-16103

Citation: Technology and Health Care, vol. 16, no. 1, pp. 19-30, 2008

Authors: Kortright, Eduardo | Rayarao, Geetha | Li, Longchuan | Anayiotos, Andreas S. | Biederman, Robert W.W. | Doyle, Mark

Article Type: Research Article

Abstract: Purpose: We sought to show that a spheroidally shaped control volume (CV), formed from a minimal MRI data set, can be used to measure regurgitant flow through a defective cardiac valve consistently and accurately under a variety of flow conditions. Materials and Methods: Using a pulsatile flow pump and phantoms simulating severe valvular regurgitation, we acquired 31 scans of two or three radially oriented slices, using a variety of flow waveforms and regurgitant volumes of 12 to 55 ml. Data sets included high- and low-resolution scans, and variable-rate sparse sampling was also applied to reduce the scan time. …An oblate spheroid was placed in the pump chamber opposite the jet and fit as tightly as possible to isomagnitude velocity contours at 25% of the velocity encoding limit. Results: Normalized regurgitant volumes (NRVs) expressed as a percentage of the pump setting were obtained from the product of the spheroid surface area with the velocities normal to it. Mean ± SD NRV values were 96.8 ± 6.6% for all scans. Imaging times in the breath-hold range were obtained using reduced resolution and variable-rate sparse sampling approaches without significant degradation in accuracy. Conclusion: In our preliminary findings, the spheroidal CV method showed clear potential for the development of a robust, clinically feasible technique for the measurement of regurgitant volume. Show more

Keywords: Regurgitant flow, velocity encoded cine, magnetic resonance imaging

DOI: 10.3233/THC-2008-16104

Citation: Technology and Health Care, vol. 16, no. 1, pp. 31-45, 2008

Authors: Slomka, Noa | Diamant, Idit | Gefen, Amit

Article Type: Research Article

Abstract: Vertebral compression fractures are a potentially severe injury, which is characteristic to osteoporotic elderly. Despite being a significant healthcare problem, the etiology of compression fractures is not fully understood, and there are no biomechanical models in the literature that describe the development of these fractures based on cancellous bone failure accumulation. The objective of this study was therefore to develop a computational model of tissue-level failure accumulation in vertebral cancellous bone, which eventually leads to compression fractures. The model predicts the accumulated percentage of broken trabeculae δ in a vertebral region of interest (ROI) over 60 years, by employing Euler's …theory for elastic buckling. The accumulated failure δ is calculated as function of the daily activity characteristics and rate of annual bone loss (RABL) with aging. An RABL of unity represents the normal bone loss attributed to aging per se, whereas RABL>1 is assumed to represent pathological bone metabolism such as osteoporosis. Simulations were conducted for a range of RABLs, to determine the effect of changes in bone metabolism on the accumulation of bone failure. Results showed that bone failure rapidly increased with RABL. Generally, trabecular failure was shown to become more severe for RABL>4. Total failure was exhibited at RABL=7.5 for the central ROI, and at RABL=8.5 for the sub-endplate ROI. We concluded that vertebral compression fractures advance monotonically between the age of 50–55 years and 70 years, and may accelerate thereafter if RABL is high (∼8). Additionally, the model identified weight lifting as the action that most dramatically accelerated the destruction of osteoporotic spinal cancellous bone. The present biomechanical model is useful for understanding the etiology of compression fractures, and potentially, depending on further experimental characterization of RABL, for considering the effects of medications that influence bone metabolism on patient prognosis. Show more

Keywords: Osteoporosis, compression fractures, trabecular bone, buckling, model

DOI: 10.3233/THC-2008-16105

Citation: Technology and Health Care, vol. 16, no. 1, pp. 47-60, 2008

Authors: Then, C. | Menger, J. | Benderoth, G. | Alizadeh, M. | Vogl, T. J. | Hübner, F. | Silber, G.

Article Type: Research Article

Abstract: Pressure sores are the most common complication associated with patient immobilization. They develop through sustained localized tissue strain and stress, primarily caused by body supports. Modifying support design can reduce the risk and extent of pressure sore development with computational simulations helping to provide insight into tissue stress-strain distribution. Appropriate material parameters for human soft tissue and support material, as well as precise anatomical modelling, are indispensable in this process. A finite element (FE) model of the human gluteal region based on magnetic resonance imaging (MRI) data has been developed. In vivo human gluteal skin/fat and muscle long-term material parameters …as well as open-cell polyurethane foam support long-term material parameters have been characterised. The Ogden form for slightly compressible materials was employed to describe human gluteal soft tissue behaviour. Altering support geometries and support materials, effects on human gluteal soft tissue could be quantified. FE-analysis indicated maximal tissue stress at the muscle-bone interface, not at the skin. Shear strain maxima were found in the muscle layer near the fat-muscle interface. Maximum compressive stress magnitude at the sacral bone depended strongly on the behaviour of the pelvic diaphragm musculature. We hypothesize that the compliance of the muscles forming the pelvic diaphragm govern the relative motion of the buttock tissue to the adjacent bone structure under compression, thus influencing tissue stress magnitudes. Show more

Keywords: Pressure sore, human gluteal soft tissue, stress and strain distribution, FE-simulation

DOI: 10.3233/THC-2008-16106

Citation: Technology and Health Care, vol. 16, no. 1, pp. 61-76, 2008